Method and apparatus for starting free-piston engines



June 7, 1960 H. JANlcKE ,9

METHOD AND APPARATUS FOR STARTING FREE-PISTON ENGINES Filed Aug. 16,1957 Inventor:

2,939,273 Patented June 7, 1960 METH D APPA ATUS. ronsmmo FREE-PISTONENGINES Hermann Jiinicke, Ahornstrass Loc'bhanrnear Munich, German"Filed Aug. 16, 1957, Ser.No. 67,717 A Claims priority, application:Germany Aug. 24, 1956; 3 Claims. CI. 60-13) The present inventionrelates to a method and apparatus for starting so-calledfree-pistonengines to which is connected a turbine which is driven by the exhaustgases of the engine, and in turn drives a compressor supplying thecompressed air required for supercharging the engine cylinder.

It is known to start free-piston engines by means of compressed airwhich is taken from a compressed air reservoir provided for thispurpose. This compressed air reservoir which serves only for starting,and the equipment necessary for recharging such reservoir, constitute animportant factor of additional expenses which is avoided by the presentinvention.

According to the invention, the starting of a freepiston engine, theengine cylinder of which is supercharged with compressed air deliveredby a compressor driven by an exhaust-driven turbine, is effected in sucha manner that the compressed air delivered by the compressor is used forstarting the engine.

In a preferred embodiment of the starting method according to theinvention the exhaust-driven turbine and the compressor coupledtherewith are first accelerated by an auxiliary starter motor toapproximately the speed at which the exhaust-driven turbine runs duringnormal operation of the free-piston engine, whereupon the compressed airdelivered by the compressor is admitted to act on the free pistons ofthe internal combustion engine as soon as the required starting pressurehas been attained.

According to a further feature of the invention a portion of thecompressed air supplied by the compressor during starting, may besupplied directly to the scavenging ports of the engine cylinder, andthrough the exhaust ports of the latter to the exhausbdriven turbine.

The invention will now be described in more detail with reference to theaccompanying drawing.

The drawing shows in diagrammatic representation, and partly inlongitudinal section, a free-piston internal combustion engine to eachpiston of which there is connected a pair of pump pistons arranged atright angles thereto.

The engine pistons 2, 2 are freely movable in the engine cylinder 1 in amanner known per se. Each of the engine pistons 2, 2 is rigidlyconnected with a return piston 5, respectively 5' which operates in anassociated return cylinder 6, respectively 6'. The return cylindersserve to return the pistons to their inner dead center position. Thework required therefor is performed by the compressed air supplied by acompressor 7. The compressor 7 which is driven by an exhaustdziventurbine 13 connected to an exhaust conduit =12,-

supplies on the one hand the compressed air for supercharging the enginethrough a conduit 9 and scavenging ports 10, and on the other hand theworking pressure for the return cylinders 28, 28' through conduits 8, 8.

Each of the engine pistons drives, through a connecting rod 3,respectively 3', a pump pair 4, 4 respectively 4', 4 which suppliespressure fluid to a hydraulic apparatus,

for example to a hydraulic motor. The arrangement and drive of suchfluid pumps in connection with free piston engines is known anddescribed for example in my co-pending U-.S.applica' tion Serial No.666,114.

The exhaust conduit 12 leading to the exhaust-driven turbine 13 isconnected to the exhaust ports 11 of the engine cylinder 1 via apressure-retaining valve 14 which maintains the pressure at apredetermined constant value during operation but valve 14 isinoperative during starting. Thus, the under pressure delivered by thecompressor into line 9 during starting can pass without reductionthrough line 12 to the turbine and assist the operation of compressor 7.I

From conduit 8, a conduit 15 leads to the housing 16 of the starting,valve which comprises a control piston 17 kept in the closed position bya spring ,18 which is set to the desired starting pressure. A conduit 19contreats the valve housing 16 with the valve housing 20 the piston 21of which actiiate's, through links 22, 23 and levers 24, 24' throttlevalves 25, 25' provided in the conduits 8, 8 respectively. The throttlevalves 25, 25' are brought into their closed position by a spring 26,when the pressure prevailing in conduit 8 drops below a predeterminedvalue after the internal combustion engine has been stopped, so thatpiston 17 closes conduit 15 under the action of spring 18, and thecompressed air contained in housing 20 escapes at the rear of piston 17through an opening 27.

Reference numeral 29 designates an electric starter motor to whichcurrent may be supplied from a battery 37 by closing a switch 36,whereby the shaft of the starter motor is displaced and its pinion 32 isbrought into engagement with a gear 31, as is common practice in motorvehicles. Gear 31 is in mesh with a gear 30 mounted on the shaft of unit7, 13, so that this unit can be accelerated to approximately operationalspeed by the motor 29.

The starting operation is as follows:

Let it be supposed that the pistons 2 and 2 are in their outer deadcenter positions. For starting the engine, switch 36 is closed so thatunit 7, 13 is accelerated approximately to the speed which correspondsto normal operation of the internal combustion engine. The compressor 7supplies on the one hand the compressed air required by engine cylinder1 through 9, 10 a portion of which air is supplied to the exhaust-driventurbine 13 through the exhaust ports 11. The pressure-retaining valve 14which may be provided is not an essential element of the engine. Valve14 is inoperative during the starting operation.

Turbine 13 brings about a retarding influence or choking during startingbecause of the outlet nozzles usually provided in the stationary part ofthe turbine to direct the air under pressure to the runner blades. Thischoking effect is assisted by the retarding efiect due to restrictions10, 11 but not by valve 14 which is inoperative during starting.

After the pressure required for starting the engine has been attained inconduits 8, 9 as well as in engine cylinder 1 and in conduit 12, thevalve 16, 17 opens, so that the compressed air acts on piston 21 whichbegins to move and opens the previously closed throttle valves 25, 25.Thereby the compressed air acts on the return pistons 5, 5' which aremoved inwards so that the internal combustion is started in the knownmanner. Switch 36 may now be opened so that starter motor 29 comes to astandstill and pinion 32 is disengaged from gear 31.

By the air pressure prevaiing on condut 15, throttle valves 25, 25' arekept open through valves 17 and 21 also during normal operation of theinternal combustion engine. After the engine has been stopped, thepistons 2 and 2" are returned to'their'outer dead center position i byany suitable means which are not "an object of the present invention.

. 1: vis, g u v .als i s u e ydraul .Q jot 2a. a

pneumatic star me us instead bfi'theele'etric' :TI claimz j L'Theombination comprising f a free-piston engine including a cylinderand'disposedtherein two' oppositely reciprocating 'ipi'stons definingbetwe'enfthem inner combustion space, each'of 'said pistons at its outer'end being providediwith an enlarged retum piston movable in an outerreturn cylinder, "an exhaust-driven turbine and an air compressorfdriven thereby, 'an'exhaust-con-f duitexte'ndingfrom said combustion'space to said'tur bine, said compressor supplying compressed airiwhichis delivered through airlines rintothe outer return cylinders foractuatingthe-return' pistons andfallso through scavenging ports into thecombustion space; pressure responsive. means responsive'to the'deliverypressure of said compressor andadapted to open said air-linesconne ctingsaid compressor to said returncylinders when said delivery pressure apredetermined value;

and an auxiliary starter motor operatively connected to saidcompressorfor starting the free-piston engine.

2. The combination as set forth in claim 1 in which the starter motor isconstructed to accelerate the exhaust-dr-iven turbine and the compressordriven thereby to approximate the speed at which said exhaust-drivenator un du n n m ra on O h free piston engine, the pressure responsivef-mean's comprising valve means adapted to be open when pressure of theair delivered by, the compressor reaches the predetermined value.

3. The combination as setforth in claim 1 in which a portion oftheairjdeliveredbythe compressor during starting enterstheinnercombustion": spacethrough the scavenging and leaves the combustion'ispace through the exhaust conduit and is fed to the exhaustdriventurbine. J

p References Cited in the file of this patent UNI TED-TSTATE S PATENTS

